1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing an LCD device for improving reflectivity.
2. Discussion of the Related Art
With development of the information society, the demand for various display devices increases. Accordingly, many efforts have been made in researching and developing various flat display devices such as the liquid crystal display (LCD), the plasma display panel (PDP), the electro luminescent display (ELD), and the vacuum fluorescent display (VFD), and some species of these flat display devices are already applied to displays of various equipment.
Among the various flat display devices, the LCD device has been the most widely used due to its advantages of thinness, lightness in weight, and low power consumption, whereby the LCD device substitutes for the Cathode Ray Tube (CRT). In addition to the mobile type LCD devices such as the display for a notebook computer, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in LCD technology with applications in different fields, research in enhancing the picture quality of the LCD device has been in some respects lacking as compared to other features and advantages of the LCD device. Therefore, in order to use the LCD device in various applications as a general display, should produce a high quality picture, for example with high resolution and high luminance within a large-sized screen while still being light weight, thin, and low power.
An LCD device displays an image or a picture by controlling the light transmittance of a liquid crystal with an electric field having a dielectric anisotropy.
The LCD device is different from display devices such as an electro luminescence (EL) device, a cathode ray tube (CRT) and a light emitting diode (LED) device. The EL, CRT and LED devices each emit light, but the LCD device makes use of ambient light as a light source.
There are two different types of LCD devices, a transmitting type LCD device and a reflective type LCD device. The transmitting type LCD device has a backlight as a light source at the rear of the LCD panel, whereby the transmitting type LCD device can display a picture image in low light surroundings by controlling the light transmittance according to the alignment of the liquid crystal. However, the transmitting type LCD device has problems in that it has high power consumption. Meanwhile, the reflective type LCD device uses ambient light as a light source, thereby having a relatively low power consumption. However, the reflective type LCD device has problems in that it cannot display a picture image in low light surroundings.
In order to solve the problems of both the transmitting and reflective type of LCD devices, a transflective LCD device is proposed. The transflective LCD device can be used as a reflective type or a transmitting type of LCD device as needed.
FIG. 1 is a cross-sectional view illustrating a related art reflective color LCD device. Referring to FIG. 1, the related art reflective color LCD device includes an upper substrate 13 having a color filter layer (not shown) and a common electrode 17, a lower substrate 11 having a thin film transistor (not shown) and a reflective electrode 16, and a liquid crystal 19 between the lower and upper substrates 11 and 13. At this time, liquid crystal molecules of the liquid crystal 19 are aligned in a predetermined direction by the electric field, i.e., the liquid crystal 19 is an optical anisotropy medium controlling the light transmittance according to the alignment of the liquid crystal molecules. Herein, it is possible to use a predetermined medium having the optical anisotropy characteristics instead of the liquid crystal 19.
In addition, plurality of medium layers are formed on external surfaces of the respective lower and upper substrates 11 and 13 to control the light polarization state. For example, a scattering film 21, a retardation film 23, and a polarizing plate 25 are sequentially deposited on the upper substrate 13. The scattering film 21 is formed to obtain a wide view angle by scattering light, and the retardation film 23 includes a first phase difference film having the characteristics of λ/4 plate to affect the light to the reflective electrode, and a second phase difference film having the characteristics of λ/2 plate.
When a voltage is not applied to the retardation film 23 in a turn-off state, the phase of the light is inversed, thereby emitting a mount of lights to the outside. Thus, an LCD panel having high luminance characteristics is formed. Also, the polarizing plate 25 only passes light having a specified polarization.
FIG. 2 is a plan view illustrating an array substrate for a reflective type LCD device according to the related art. As shown in FIG. 2, a plurality of gate lines 33 are formed on a lower substrate 11 in one direction at fixed intervals, and a plurality of data lines 36 are formed in perpendicular to the gate lines 33 at fixed intervals to define a plurality of pixel regions. A matrix type pixel electrode (reflective electrode) 16 is formed in each pixel region P defined by crossing the gate lines 33 to the data lines 36. Then, a plurality of thin film transistors T are formed that are switched according to a signal on the gate line 33 to transmit the signal on the data line 36 to the pixel electrode (reflective electrode) 16.
At this time, the thin film transistor T includes a gate electrode 27 extending from the gate line 33, a gate insulating layer (not shown) on the entire surface of the lower substrate 11, a semiconductor layer 30 on the gate insulating layer above the gate electrode 27, a source electrode 29 extending from the data line 36, and a drain electrode 31 opposite to the source electrode 29. The drain electrode 31 is electrically connected to the pixel electrode 16 through a contact hole 35.
Meanwhile, the lower substrate 11 is bonded to an upper substrate (not shown) with a predetermined space.
The upper substrate includes a black matrix layer preventing light from leaking. The black matrix layer has an opening corresponding to the pixel region P of the lower substrate 11, R/G/B color filter layers for displaying colors, and a common electrode for driving the liquid crystal with the pixel electrode (reflective electrode) 16.
The predetermined space is maintained between the lower and upper substrates 11 and 13 by spacers, and then the lower and upper substrates 11 and 13 are bonded to each other by a sealant having a liquid crystal injection hole. Subsequently, the liquid crystal is injected between the lower and upper substrates 11 and 13 through the liquid crystal injection hole.
FIG. 3 is a cross-sectional view illustrating an LCD device taken along line II-II′ of FIG. 2. Referring to FIG. 3, a conductive metal material such as aluminum Al, aluminum alloy, molybdenum Mo, tungsten W, or chrome Cr is deposited on the lower substrate 11, and then selectively patterned by photolithography, thereby forming the gate line 33 and the gate electrode 27 extending from the gate line 33. Then, a gate insulating layer 28 is formed by an inorganic insulating material such as silicon nitride SiNx or silicon oxide SiOx or by an organic insulating material such as BenzoCycloButene BCB or acryl. Subsequently, an amorphous silicon including pure amorphous silicon and impurities is formed on the entire surface of the lower substrate 11 including the gate insulating layer 28, and then selectively removed by photolithography, thereby forming the island-shaped semiconductor layer 30 on the gate insulating layer 28 above the gate electrode 27.
Next, the aforementioned conductive metal layer is deposited on the entire surface of the lower substrate 11 including the semiconductor layer 30, and then selectively removed by photolithography, whereby the data line 36 is formed substantially perpendicular to the gate line 33. The source electrode 29 is formed on the semiconductor layer partially overlapping the gate electrode 27, and the drain electrode 31 is formed apart from the source electrode 29. Then, a passivation layer 36 is formed of an organic insulating material such as BenzoCycloButene (BCB) or acrylic resin, and then selectively removed to expose the drain electrode 31 by photolithography, thereby forming the contact hole 35. An opaque metal having great reflectivity such as aluminum Al is deposited on the entire surface of the passivation layer 36 and contact hold 35 of the lower substrate 11 and then selectively removed by photolithography, whereby the pixel electrode (reflective electrode) 16 is formed in the pixel region P electrically connected to the drain electrode 31 through the contact hole 35.
The method for manufacturing the related art LCD device will be described with reference to FIGS. 4-6. FIG. 4 is a plan view illustrating the related art LCD device having the reflective electrode including a protrusion, and FIG. 5 is a cross-sectional view illustrating the related art LCD device taken along line IV-IV′ of FIG. 4.
As shown in FIG. 4 and FIG. 5, the thin film transistor T (gate electrode 27, gate insulating layer 28, source electrode 29, drain electrode 31 and semiconductor layer 30), is formed on the lower substrate 11, and the passivation layer 36 is formed on the entire surface of the lower substrate 11 including the thin film transistor T. Then, a plurality of protrusions 37a of photoacryl material are formed on the passivation layer 36 at fixed intervals. The plurality of protrusions 37a are formed on the entire surface of the lower substrate 11 including the thin film transistor T at fixed intervals to improve an reflection angle of light.
The reflective electrode 16 is formed on the passivation layer 36 having the protrusions 37a and electrically connected to the drain electrode 31 of the thin film transistor T. The reflective electrode 16 has an uneven surface because of the protrusions 37a formed on the passivation layer 36. Accordingly, if incident light is reflected and emitted, the reflective electrode 16 condenses the light incident on the protrusions 37 from different angles, and emits the condensed light in a predetermined angle. An organic insulating layer 38 is formed on the entire surface of the lower substrate 11 including the protrusions 37a, and the reflective electrode 16 is formed on the organic insulating layer 38.
FIG. 6A to FIG. 6E are cross-sectional views illustrating manufacturing process steps of the related art LCD device taken along line IV-IV′ of FIG. 4.
As shown in FIG. 6A, the passivation layer 36 is formed on the entire surface of the lower substrate 11 including the thin film transistor T and the photoacryl resin 37 is deposited on the passivation layer 36.
In FIG. 6B, the photoacryl resin 37 is patterned by an exposure and developing process, thereby forming a plurality of photoacryl resin patterns 37b at fixed intervals.
In FIG. 6C, the plurality of photoacryl resin 37b are reflowed by a heat treatment, thereby forming a plurality of hemisphere-shaped protrusions 37a. 
In FIG. 6D, the organic insulating layer 38 is formed on the entire surface of the lower substrate 11 including the hemisphere-shaped protrusions 37a. Next, the organic insulating layer 38 and the passivation layer 36 are selectively removed by photolithography to expose the drain electrode 31 of the thin film transistor, thereby forming the contact hole 35.
In FIG. 6E, the opaque metal layer having great reflectivity, such as aluminum Al, is deposited on the entire surface of the lower substrate 11 including the contact hole 35 and then selectively removed by photolithography, whereby the reflective electrode 16 is formed in the pixel region in contact with the drain electrode 31. The reflective electrode 16 is the pixel electrode. The reflective electrode 16 has an uneven surface because of the plurality of protrusions 37a. 
However, the method of manufacturing the related art LCD device has the following disadvantages. In the manufacturing method for the related art LCD device, photoacryl is used for forming the reflective electrode having the uneven surface, and a heat treatment has to be performed, whereby the manufacturing process is complicated and the manufacturing cost increases.